* feat(coding-agent): add before_provider_headers extension hook
Extensions can already rewrite the request payload through before_provider_request, but there is no way to adjust the outgoing HTTP
headers of a provider call. This hook fills that gap for cases like request tracing, session correlation, or tenant routing.
Handlers mutate the headers map in place - a null value deletes a header - and the return value is ignored, so a handler cannot accidentally drop auth or attribution headers by
forgetting to spread.
* docs(coding-agent): document before_provider_headers extension hook
Add the before_provider_headers section and lifecycle-diagram entry to
extensions.md; drop the now-superseded proposal file.
* feat(coding-agent): add InlineExtension type for named inline extension factories
* test(coding-agent): update utilities and add regression test for InlineExtension
The Message types require content to always be present, but untyped JS
extension tools, hand-built histories, and old or hand-edited session
files can violate that contract, crashing rendering, compaction, and
provider request conversion with 'content is not iterable'.
Normalize null/missing content to an empty array at the ingestion
boundaries instead of guarding every consumer:
- transformMessages (choke point before every provider request)
- createToolResultMessage in the agent loop
- session entry loading (message and custom_message entries)
- extension custom messages (sendCustomMessage, before_agent_start)
- message_end extension replacements
fixes#6259, fixes#6276
session_before_compact and session_compact now carry
reason ("manual" | "threshold" | "overflow") and willRetry, matching
what the RPC protocol already exposes via auto_compaction_start/end.
Extensions can now distinguish manual /compact from threshold
auto-compaction and overflow recovery through the public API instead
of monkeypatching AgentSession internals.
Avoid quadratic path construction when walking deep session branches. On a 600k-entry pathological session, path construction improved from about 20.3s with Array.unshift() to about 35ms with push() plus reverse().
Refs #5804.
Vegard Stikbakke