mirror of
https://github.com/openprose/prose.git
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dan
624e75ad89
* Refresh OpenProse skill conventions * Align OpenProse skill with service system conventions * Fix OpenProse PR review inconsistencies * Clarify OpenProse state backend loading * Enforce OpenProse smoke run state gate
96 lines
3.5 KiB
Markdown
96 lines
3.5 KiB
Markdown
---
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name: fallback-chain
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kind: pattern
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---
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# Fallback Chain
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Try delegate A. If it fails, try B. If B fails, try C. Ordered list of fallbacks with decreasing preference.
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### Metadata
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- `version`: 0.1.0
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- `role`: coordinator
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### Slots
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- `chain`
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### Config
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- `failure_criteria` (string, default: none): Optional description of result-level failure conditions
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### Invariants
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- Chain entries run sequentially in declared preference order
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- Each delegate receives the original brief, not failure context from earlier attempts
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- The pattern stops immediately on the first success
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- If every delegate fails, the result is `null` and failure history includes every attempt
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### Shape
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- `self`: try each delegate in order, return first success, stop on success
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- `delegates`:
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- `fallback_1..fallback_N`: attempt the task
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- `prohibited`: trying the next fallback when the current one succeeded
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### Requires
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- Pattern instance receives:
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chain: string[] -- ordered list of service or system names (first = most preferred)
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task_brief: string -- the task (same brief goes to each attempt)
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failure_criteria: string -- (optional) declarative description of what constitutes failure.
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Default: only thrown errors count as failure.
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### Ensures
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- Delegates are tried sequentially in chain order
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- First successful result is returned immediately — no further delegates are tried
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- Each delegate receives the ORIGINAL brief — no failure context from prior attempts
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- If all delegates fail: return null with full failure history
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- `result`: the winning result, or `null`
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- `winner`: the winning delegate name, or `null`
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- `attempts`: number of delegates tried
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- `failure_history`: reasons for each failed attempt
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### Delegation
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```prose
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let failure_history = []
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for delegate in chain:
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try:
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let candidate_result = call delegate
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task_brief: task_brief
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if failure_criteria says candidate_result is a failure:
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record { delegate: delegate, reason: "matched failure_criteria" } in failure_history
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continue
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return {
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result: candidate_result,
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winner: delegate,
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attempts: "number of attempted delegates",
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failure_history: failure_history
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}
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catch as error:
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record { delegate: delegate, reason: error } in failure_history
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return {
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result: null,
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winner: null,
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attempts: chain.length,
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failure_history: failure_history
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}
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```
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### Notes
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Each delegate receives the original brief with no modification. Unlike `retry-with-learning`, fallback-chain does not pass failure context between attempts — each delegate gets a clean start. The assumption is that different delegates have different capabilities, not that the same delegate needs better instructions.
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The chain order expresses preference. Put the best, most capable, or cheapest delegate first. Later delegates are fallbacks for when preferred options fail.
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Different from `retry-with-learning`: retry retries the SAME service with enriched failure context. Fallback-chain tries DIFFERENT services with the original brief. A search service that returned no results should be retried with broader terms (retry-with-learning). A search service that is down should be replaced with an alternative (fallback-chain).
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Different from `race`: race tries all candidates simultaneously. Fallback-chain tries them sequentially, only advancing on failure. Use fallback-chain when later candidates are expensive and should only run if cheaper ones fail. Use race when all candidates are worth trying in parallel.
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